New research strengthens the case against soda and other sugary drinks as being part of the obesity epedemic.

Richard Drew/Associated Press file photo

New research strengthens the case against soda and other sugary drinks as being part of the obesity epedemic.

New research powerfully strengthens the case against soda and other sugary drinks as culprits in the obesity epidemic.

A huge, decades-long study involving more than 33,000 Americans has yielded the first clear proof that drinking sugary beverages interacts with genes that affect weight, amplifying a person’s risk of obesity beyond what it would be from heredity alone.

This means that such drinks are especially harmful to people with genes that predispose them to weight gain. And most of us have at least some of these genes.

In addition, two other major experiments have found that giving children and teens calorie-free alternatives to the sugary drinks they usually consume leads to less weight gain.

Collectively, the results strongly suggest that sugary drinks cause people to pack on the pounds, independent of other unhealthful behavior such as overeating and getting too little exercise, scientists say.

That adds weight to the push for taxes, portion limits such as the one just adopted in New York City, and other policies to curb consumption of soda, juice drinks and sports beverages sweetened with sugar.

Soda lovers do get some good news: Sugar-free drinks did not raise the risk of obesity in these studies.

“You may be able to fool the taste” and satisfy a sweet tooth without paying a price in weight, said an obesity researcher with no role in the studies, Rudy Leibel of Columbia University.

The studies were presented Friday at an obesity conference in San Antonio and were published online by the New England Journal of Medicine.

The gene research in particular fills a major gap in what we know about obesity. It was a huge undertaking, involving three long-running studies that separately and collectively reached the same conclusions. It shows how behavior combines with heredity to affect how fat we become.

Having many of these genes does not guarantee people will become obese, but if they drink a lot of sugary beverages, “they fulfill that fate,” said an expert with no role in the research, Jules Hirsch of Rockefeller University in New York. “The sweet drinking and the fatness are going together, and it’s more evident in the genetic predisposition people.”

Sugary drinks are the single biggest source of calories in the American diet, and they are increasingly blamed for the fact that a third of U.S. children and teens and more than two-thirds of adults are obese or overweight.